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Standard Horizon HX870 Features

Posted: Fri Apr 26, 2019 11:44 am
by MattFL
I'm hoping this topic can help people like me understand the features of the HX870 radio.

At the moment the power saving features are not clear to me. I need to be filled in on some details on the following which are not described in the manual:

  • For the GPS power saving feature, I assume that the higher you turn the battery saving, the less frequently the GPS updates its position. Does anyone know the exact correlation between battery saving setting and rate of update? Does no power saving result in position updates every second, 50% setting indicate position updates every 30 seconds?
  • For the receiver battery save feature, based on this post ( the battery save setting is basically a duty cycle setting. For example, at 50% battery saving the radio will sleep for 100ms then wake for 100ms (50% duty cycle). Does this feature stay active during channel scan? I set it to 90% saving, which in theory would sleep the radio 900ms (nearly a full second) then wake for 100ms to check for signal. However channel scan appears visually to be scanning through channels at full speed, which cannot be if the receiver is truly at 10% duty cycle!?

To test battery life I fully charged the radio, turned it on this morning at 6:30am with GPS battery saving at 75% and receiver battery saving at 70%, and scanning my 7 favorite channels, and played with the menus for probably 30 minutes. It is now 5 hours later and the display is showing 2/3 remaining, but time will tell how fast it goes down from here. The front of the radio remains warm which tells me it's using a lot of power for something.

Re: Standard Horizon HX870 Features

Posted: Fri Apr 26, 2019 12:03 pm
by jimh
The rate at which a particular GPS receiver can produce a position fix update varies with the receiver. For GPS receivers where the motion of the GPS receiver itself is slow, an update rate of one-per-second (1-Hz) is probably more than sufficient. Once the receiver has power and has acquired satellites, it will update its position fix at the rate it was designed for.

If a GPS receiver has been switched off for a long period of time, then the receiver will not have any recent information about which satellites are in view. The lack of that information will increase the time required for the GPS receiver to get its initial position fix.

I don't know the precise strategy used in the HX870 radio with regard to operating the GPS receiver in a manner to save battery life. If the GPS receiver has not had operating power for a while, it will take longer for it to acquire a position fix. If the GPS receiver is repeatedly powered on intermittently to get a new position fix and update its knowledge of satellites in view, it may acquire the position fix faster because the data it has stored about satellites in view will be more likely to be accurate.

In general you could say that a GPS receiver in an HX870 that was operating more frequently would be able to get a position fix faster than if that receiver had been switched off for a long time. The trade-off in improved battery life is probably going to be a longer time to first position fix.

Re: Standard Horizon HX870 Features

Posted: Sat Apr 27, 2019 10:43 am
by jimh
ASIDE on the behavior of GPS receivers: the data about satellite orbits is sent by the GPS system in the navigation message. The data rate of the navigation message is very low, and it takes about 12-minutes for the entire message to be sent. Until a GPS receiver has this message, it does not know what satellites will be in view and what their precise location will be,

A GPS receiver that had no hints about what satellites are in view at the moment it is powered on--a situation called a cold start--might take a long time to acquire a position fix. The reason for the delay in acquiring a position fix is due to the receiver having to methodically search for signals from all possible satellites. In GPS that means that any of 32 possible satellites could be in view, and each must be discovered by listening for a particular PRN code. A further complication is the Doppler Shift in frequency at the receiver, resulting from the apparent motion between the satellite and the receiver. If the GPS receiver does not have hints if the satellite is approaching the GPS receiver or receding from the GPS receiver, it has to search a wide range of frequencies to find the signal. All of this adds up to longer delays in acquiring signals from at least three satellites, the minimum number needed for a two-dimension (latitude and longitude) position fix.

Once a GPS receiver obtains one satellite, it can begin to receive the navigation message from that satellite. The message contains information about the current orbits of all satellites in the GPS constellation. The data about GPS satellite orbits is called the Ephmerides.

Some manufacturers of GPS chips enhance the performance of their receivers by adding on-chip memory that stores data about the Ephemerides on the chip, so the GPS receiver will have some information at start-up, although the might be minutes, hours, or days old. Some chips can also make predictions of future satellite positions based on older orbit data, generating their own predicted Ephmerides that can be useful in finding satellites in view and getting the latest navigation message from them.

And some chips have very many receivers (often referred to in boating literature as "channels") which can decrease time to first fix by using all receivers to hunt simultaneously for satellites in view.

In the case of terrestrial GPS receivers associated with a cellular telephone, an additional protocol called ASSISTED GPS or A-GPS can drastically reduce the time to first fix. In A-GPS the navigation message is sent over a high-speed cellular data link from the cellular network to the cellular telephone. Since the cellular telephone is always connected to its cellular network when operating, this means there will always be a current navigation message available. A GPS receiver in a cellular telephone that uses A-GPS can get the navigation message sent by the cellular network and immediately know what satellites are in view. In the case of power management in "smartphones" the GPS chip is often not powered on at all unless the user needs to get a position fix. The chip can be powered on and with the help of A-GPS have a position fix in a second or two. This sort of power management is used to extend battery life in smartphones.

A-GPS is not used in marine GPS receivers because A-GPS only works when the GPS receiver is paired with a cellular telephone network, and ships are often too far from land for cellular network reception.

Re: HX870

Posted: Mon Apr 29, 2019 10:14 am
by MattFL
I just purchased the HX870 and I haven't had the opportunity to try the polling feature yet. The documentation indicates that [the HX870] does support [polling and polling acknowledgement].

Automatically poll the GPS position of a ship using DSC

The owners manual in section 10.9 "POLLING CALL" states

The HX870 has the capability to track another vessel.

It goes on to describe how to transmit a polling call to another vessel.

The HX870 also supports group polling, or tracking the location of a group of vessels. Section 12 "GM OPERATION" in the manual opens with:

The GM (Group Monitor) feature of the HX870 utilizes the same system as the DSC Group call and Auto Position Polling, to display the group members' locations.

It goes on to describe how to use the feature.

Re: HX870

Posted: Mon Apr 29, 2019 8:04 pm
by jimh
Let us know when you can confirm the other anecdotal reports that the HX870 really has those features.

Re: HX870

Posted: Mon Apr 29, 2019 8:41 pm
by MattFL
The menus appear to be there on the radio, I just need to convince some buddies to get their radios fully functional with MMSI numbers so I can give it a try.

Re: Standard Horizon HX870 Features

Posted: Mon May 13, 2019 11:12 am
by MattFL
I've used the Standard-Horizon HX870 handheld radio a couple of times now. I will commenting on some good and bad features.

Battery life so far has seemed adequate for general daily use. After seven hours in the boat scanning channels it appears to have roughly half the battery capacity left.

The navigation computer works, but is definitely bare bones. The biggest missing feature is the ability to see the distance to each waypoint at a glance, or see the waypoints nearest you. To see distance to each waypoint, you have to begin navigation to that waypoint, then you can see the distance. This is not convenient when you have a list of 20 favorite waypoints (like ship wrecks or underwater rocks) and you don't remember their exact locations by name alone that is, no fish here, let’s go to the nearest underwater structure. Or, which of these 20 marked ledges and shipwrecks is the nearest?

During navigation the screen zoom changes automatically based on the distance to your target which is nice. Wiith the GPS battery saving set at 70%, the GPS position updates frequently enough for general fishing use. It is no where near as nice as a typical console mount GPS and chart plotter, but was great to have on my buddies boat as I had lots of fishing locations marked that he didn't have. The HX870 got us there.

The HX870 has two channel scan modes; priority scan, and regular scan. For example, you have set to scan channels 16, 68, 69, 70. In priority mode it scans your priority channel (16 by default) in-between every channel. So scanning would go 16-68-16-69-16-70. And when it picks up traffic on, say, 68, it will periodically check back for traffic on 16. If you're listening to a conversation on 68, audio cuts out for a fraction of a second every second or two as it checks back on 16.

In regular scan mode it just goes through the channels 16-68-69-70-16 and does not check back on the priority channel, so audio does not cut out. Having used it one day in each mode, my perception is the battery life is slightly better when in regular scan mode, but I don't have any hard numbers to back this up so it could be all in my mind.

I still haven't used the DSC features yet. More info to come.

Re: Standard Horizon HX870 Features

Posted: Tue Jun 18, 2019 8:56 pm
by MattFL
I can confirm that the DSC calling and position request works on the HX870. My buddy bought the same radio and we just tried it. Initiating a DSC call makes the other radio ring and that user has the option to answer. Upon answering both radios automatically switch to the agreed upon channel. I did not try position tracking (we were in my driveway), but position request works great. When sending a DSC position request the other radio immediately responds with the position.

The person sending the request then has the option to save his buddy’s position as a waypoint, and optionally navigate to that waypoint. The remote radio indicates that it responded to a position request.

Re: Standard Horizon HX870 Features

Posted: Sat Jun 22, 2019 4:13 pm
by jimh
Thank you for the report on the features of the HX870 appearing to work.

I want to note that although the HX870 is a handheld radio, it complies with CLASS-D ratings, which are usually associated with fixed mount radios. However, in DSC the CLASS-D specification DOES NOT require position polling. That is not a mandatory feature for CLASS-D rated radios. While many manufacturers of CLASS-D DSC radios provide position polling features, and this seems to be the normal expectation for a Class-D radio, my understanding of the ITU-R M.493 document that describes the various classes of DSC radios is that the recommendation does not require the feature in a Class-D rated radio.